This invention relates to an electric converter motor of synchronous design which is connected to a power network via a frequency converter and which has a rotor with a field winding which is supplied from a DC source.
Converter motors of this kind are described, for instance, in the book of Siemens Aktiengesellschaft by Erich Eder "Stromrichter zur Drehzahlsteuerung von Drehfeldmaschinen (Industrieelektronik)", Part 4, "Der Stromrichtermotor," particularly on page 20. Converter motors of this type retain the simple design of a synchronous machine, yet can be controlled like a DC machine. Various known types of frequency converters, such as direct converters or converters having an intermediate DC link, can be connected between the power network and the machine. Suitable control means bring about the desired operating behavior of the machine.
Converter motors of this type, in the higher power ratings, are particularly useful as hoists. When used in a hoist, the machine must remain excited continuously, even while at standstill, so that it can be started up at any time without any delay for the building up of the field. However, the constant supply of field current to the field winding of the rotor, via the brushes and slip rings, while the machine is at standstill, subjects the brushes of the converter motor to increased wear.